1. Field of the Invention
The present invention relates to solar panel testing, and in particular to an apparatus for providing uniform light intensity during solar panel testing.
2. Description of the Related Art
Spacecraft use solar panels to provide electrical power for spacecraft operation and the charging of batteries. A solar panel is made from a number of individual photovoltaic cells, which produce electrical current in response to solar energy. Reliability in the testing of solar panels is very important to both solar panel manufacturing and spacecraft operation.
Currently, solar panel reliability and performance are characterized using a test configuration such as a large area pulse solar simulator (LAPSS). Often, there is a fine line between acceptable and unacceptable panels. Therefore, tests used to characterize cell performance must be precise and consistent. Precision and consistency are the keys for determining manufacturing yield and field reliability of the solar panels. Manufacturing yield refers to the number of tested and acceptable solar panels that were produced in a production run of a large number of solar panels. Additionally, correlation and repeatability between test results of different test configurations is desirable, i.e., if a particular solar panel fails in a first test configuration, that panel should also fail in a second test configuration.
Advances in solar panel and solar cell technology have yielded larger and more efficient solar panels. Typically, solar panels have fifty or more circuits, and the position of the circuit on the panel should not affect the power generated by the circuit. These advances make precision and consistency in product testing even more important because a small difference in light intensity can yield a significant difference in current produced by the solar panel.
A test configuration such as a LAPSS system uses light sources, such as xenon flash tubes, a series of baffles, and a test bed for measuring the performance of a solar panel. When the light sources illuminate the solar panel, the test bed reads the voltages and currents produced by the panel. A uniform light source is required to prevent cell xe2x80x9chot spotsxe2x80x9d where light intensity is non-uniformly high and xe2x80x9ccold spotsxe2x80x9d where light intensity is non-uniformly low. Hot spots occur on the panel on the portion of the solar panel that is directly aligned with the light source. Conversely, cold spots occur on the portion of the solar panel that is near the fringe of the light source. Hot spots and cold spots make accurate and repeatable measurements difficult due to the non-uniform illumination of the solar panel. Currently, light sources, such as those used in a LAPSS system, provide reasonably uniform light intensity, but do not take any measures to provide uniform light intensity. Additionally, as solar panel sizes and efficiency increase, current test configurations are unable to illuminate the solar panel with the required light uniformity, thereby magnifying the problems of test reliability and repeatability. Many test configurations require a large panel under test to be moved many times during testing to illuminate sections of the panel with a reasonably uniform light source. The requirement of moving a panel under test limits test accuracy and repeatability, which increases manufacturing cost and time.
It can be seen that there is a need in the art for a highly uniform light intensity testing device. It can also be seen that there is a need in the art for a light intensity device having increased reliability and repeatability of test results, thereby accurately predicting the field reliability of solar panels. It can also be seen that there is a need in the art for a device that decreases the manufacturing cost and time to produce solar panels.
To address the requirements described above, the present invention discloses a method and apparatus for filtering light to provide a uniform light density at the device under test. An apparatus in accordance with the present invention comprises a transparent sheet, substantially transparent at a wavelength region of interest, and a line pattern, printed on a first side of the transparent sheet. The line pattern selectively blocks a portion of light transmitted through the glass sheet to create a substantially uniform light intensity for the transmitted light.
An object of the present invention is to provide a highly uniform light intensity testing device. Another object of the present invention is to provide a light intensity device having increased reliability and repeatability of test results, thereby accurately predicting the field reliability of solar panels. Another object of the present invention is to provide a device that decreases the manufacturing cost and time to produce solar panels.